tailcfg,types/netmap: add (visible) Services to SelfNode Caps (#19335)

Updates #40052

Signed-off-by: Adriano Sela Aviles <adriano@tailscale.com>

types/netmap/netmap.go

@@ -146,6 +146,27 @@ func (nm *NetworkMap) GetIPVIPServiceMap() IPServiceMappings {
 	return res
 }
 
+// Services returns the Services visible (accessible) to this node,
+// decoded from [tailcfg.NodeAttrPrefixServices]+serviceName entries in the
+// self node's CapMap. Returns nil if nm is nil or SelfNode is invalid.
+func (nm *NetworkMap) Services() map[tailcfg.ServiceName]tailcfg.ServiceDetails {
+	if nm == nil || !nm.SelfNode.Valid() {
+		return nil
+	}
+	result := make(map[tailcfg.ServiceName]tailcfg.ServiceDetails)
+	for cap := range nm.SelfNode.CapMap().All() {
+		if !strings.HasPrefix(string(cap), string(tailcfg.NodeAttrPrefixServices)) {
+			continue
+		}
+		svcs, err := tailcfg.UnmarshalNodeCapViewJSON[tailcfg.ServiceDetails](nm.SelfNode.CapMap(), cap)
+		if err != nil || len(svcs) < 1 {
+			continue
+		}
+		result[svcs[0].Name] = svcs[0]
+	}
+	return result
+}
+
 // SelfNodeOrZero returns the self node, or a zero value if nm is nil.
 func (nm *NetworkMap) SelfNodeOrZero() tailcfg.NodeView {
 	if nm == nil {